The present invention relates to an elevator installation with an elevator car, which by means of a drive unit can be caused to move in an elevator hoistway. The elevator installation can be controlled by a control unit. To monitor the status of the elevator installation sensors are also provided, each of which is connected via an assigned bus node to a data bus and thereby to the control unit. In addition, the invention relates to a monitoring system for an elevator installation, which comprises several bus nodes. The bus nodes are connected via a data bus to a control unit, there being assigned to each bus node a sensor. The sensor connected to the bus node is provided for the purpose of monitoring the status of the elevator installation.
In prior art elevator installations, safety contacts are used to detect the status of the elevator installation. Conventional elevator installations use safety contacts which are connected to each other in series, in an operable status of the elevator installation all safety contacts being closed, so that a positive status signal from the elevator installation can be evaluated in a control unit. Disadvantageous with such manner of connecting the safety contacts is that no diagnosis is possible as to whether one or more safety contacts are faulty. Consequently, no suitable measures can be taken by the control unit to control the elevator installation. Moreover, with such manner of connecting the safety contacts, no identification of the safety contacts is possible, and it is also impossible to transmit further information about intermediate statuses or counter values, etc.
Nowadays, safety contacts connected in such manner are frequently replaced by bus systems to which the safety contacts are connected. These bus systems must satisfy the special safety requirements for elevator installations.
In patent document WO 03/020627 A1 an elevator system is described in which detection means are arranged which, in case of a fault in the area of the hoistway doors or car doors, a control provides fault information regarding the type of fault and location of the fault. The control is therefore able to trigger a situation-dependent safe reaction which takes into account the type of fault, the location of the fault, and information about the status. The detection means which comprise, for example, a circuit-opening switch, a circuit-completing switch, a Hall sensor, etc., are connected to a control unit of the elevator installation via a bus system. To adapt this bus system to the safety requirements, use is made of, for example, distributed sensors, there being provided in each case two or more sensors for mutual monitoring or mutual support. It is further foreseen that should a fault occur, the detection means are set into a safe status so as not to affect the elevator system negatively. The detection means are connected to the bus system via bus nodes, the safety of the bus nodes being improved by built-in redundancy which increases the safety of the entire system.
Disadvantageous with such built-in redundancy is that a bus node can also transmit a faulty signal to the control even though the sensor assigned to this bus node detects a fault-free or operable status of the elevator installation and no faulty status is in fact present.